The present invention relates to lower leg prostheses and methods of assembly and alignment of lower leg prostheses and more particularly to an improved apparatus and method of assembly and alignment.
Traditionally there are two types of lower leg prostheses, an external or exoskeletal apparatus and an internal or endoskeletal apparatus. The exoskeletal apparatus consists of a rigid leg component shaped in the appearance of the external human leg, attached to a foot. Traditionally, the leg component was constructed of solid wood, but now it is more commonly constructed of a resin or lightweight composite material formed around a solid structural foam interior. The composite laminate leg component is extremely lightweight, strong, and capable of supporting very heavy loads. The leg component is attached to the limb of a person through a socket. The,leg component is attached to an artificial foot through a block in the ankle area. The ankle block is usually solid wood or structural foam and contains a fastening mechanism such as a bolt and nut fastener to attach the artificial foot and the ankle block is usually permanently attached to the leg portion through the laminate of the leg component.
The method of forming the exoskeletal leg apparatus and aligning the socket and foot for a particular patient traditionally involves an initial bench alignment based on the experience of the prosthetist constructing the apparatus. The alignment of the apparatus is extremely important to the effectiveness and comfort of the finished device. After the leg portion is cast and attached to the ankle block further alignment of this portion is impossible without cutting the cast portion and re-constructing it. The only adjustment easily made by the prosthetist after forming the exoskeletal leg is the minor adjustment of foot rotation made possible through the foot fastener. Thus, due primarily to the alignment difficulty, the modem trend has been away from the exoskeletal leg prosthesis toward a more adjustable endoskeletal leg.
The endoskeletal leg apparatus comprises a series of tubes, simulating the bones of the leg, connected via adjustable components to the artificial foot and covered by a cosmetic cover to look like a human leg. The endoskeletal components are traditionally lightweight metals interconnected with fasteners and adjustable components. The advantage of the endoskeletal leg is that all of the components remain adjustable and are easily maintained and replaced if necessary. The components have also been standardized by many manufacturers for easy interchangeability and modularity. The main advantage of the endoskeletal apparatus is the ability for the prosthetist to align the leg by adjusting the components after the leg is statically and dynamically loaded by the end user during a fit test process. The process includes attaching a completely assembled apparatus including a foot to a user and allowing the user to stand and walk on the leg to determine the proper alignment. During this process, minute adjustments are made perfecting the alignment of the leg resulting in a more comfortable and effective prosthesis. The disadvantage of the endoskeletal leg is its relative high cost, its weight, its complexity, its noise potential due to multiple interconnected metal components, its mechanical appearance, and its lower strength capabilities as compared to the exoskeletal apparatus.
Thus what is desired is an improved apparatus and method of constructing and aligning an exoskeletal leg prosthesis.